Organophosphates pesticides (OP) are among the most widely applied pesticides worldwide and in Washington state. In adults, OPs are recognized to act as neurotoxicants through their ability to inhibit the enzyme, acetylcholinesterase (AChE). In the developing organism it is still unknown whether OP-induced developmental neurotoxicity is a consequence of AChE inhibition. Increased reports from child cohort studies suggest gestational exposures to pesticides are of public health concern. Current risk assessment and management strategies may not be optimal with the use of AChE inhibition as a regulatory anchor. This project will examine the relationship between AChE inhibition and neurotoxicity in depth, across pre- and postnatal developmental life stages. The overall hypothesis of our proposal is that pesticide exposure alters neurodevelopment and behavior in rodents by interfering with cellular pathways controlling proliferation, differentiation and apoptosis in the CNS during critical windows of susceptibility and that these mechanisms are independent of AChE inhibition. Using in vitro neurodevelopmental-stage specific models for both pre and postnatal developmental periods, we propose to assess the role of OP-induced oxidative stress and its consequential impact on these important cellular pathways, which underlie CNS development. The specific aims are: (l)to investigate the direct effects of OPs on neurite outgrowth, neuronal proliferation and viability in neurodevelopment-stage specific in vitro models (human stem cells, mouse neuronal precursor cells, and rodent hippocampal neurons);(2)to elucidate the impacts of OP-induced oxidative stress and effects on neurogenesis; (3)to examine developmental stage specific OP impacts on proliferation and differentiation gene expression pathways; and(4) to investigate OP effects on glial-neuronal communication. These proposed experiments will provide significant new insight into the mechanisms of OP-induced neurotoxicity and the role of AChE inhibition during pre- and post-natal neurodevelopment. Working closely with the Biostatistics, Modeling and Risk Characterization Facility Core, results from these studies will be integrated and translated into developing biological and pathway based models relevant for risk assessment across developmental periods and across species.